This achievement is obtained toward the end-middle of Act 4 in the main campaign. Through this section of the game you're fighting Swarm
*** Spoiler - click to reveal ***in a bid to plant beacons for the UIR Hammer of Dawn satellite launched at the end of Act 3. You also encounter the new Queen of the Locust/Swarm which happens to be a really ugly looking Reyna from Gears 4.
Act 4 only has two chapters which are "Homefront" and "The Fall," placing this plot point
The IGN guide not outlines what all is in these two chapters but also shows where all the collectibles and intractables should be.
https://www.ign.com/wikis/gears-of-war-5/Act_IV